High-frequency power transformer



Jan. 2, 1945. w. c. RUDD HIGH FREQUENCY POWER TRANSFORMER Filed June 15, 1942 4 Sheets-Sheet l I W d w a OAW/ 4 INVENTOR. m/ALL/l CE C.Z?UDD.' BY 5 4 M Jan. 2, 1945. w Q RUDD HIGH FREQUENCY POWER TRANSFORMER Filed June 15, 1942 4 Sheets-Sheet 2 A TTORNEVS Jan. 2, 1945. w. c. RUDD HIGH FREQUENCY POWER TRANSFORMER 4 Sheets-Sheet 3 Filed June 15. 1942 INVENTOR.

7 MAL i C: C. E000 BY M W M ATTORNEYS Jan. 2, 1945. w. c. RUDD HIGH FREQUENCY POWER TRANSFORMER Filed June 15, 1942 4 Sheets-Sheet 4 Mig ATTORNEYS Patented Jan. 2, 1945 HIGH-FREQUENCY POWER TRANSFORMER Wallace 0. Rudd, Yonkers, N. Y., assignor to Induction Heating Corporation, New York, N. Y., a corporation of New York Application June 15, 1942, Serial No. 447,002

' Claims. (01. 175-361) This invention relates to high frequency transformers oi. types capable of use for substantial amounts of power.

The objects of the invention include the provision of highly dependable transformers of the above indicated type, in which the working temperatures and power losses will be low, and which are oi. a simple inexpensive construction readily manufactured without requiring especially skilled workmen or special tools, materials or equipment.

Various further and more specific objects, features and advantages will more clearly appear from the detailed description given below taken in connection with the accompanying drawings which form a part of this specification and illustrate merely by way 01' example, preferred forms of the invention. The invention consists in such novel features, arrangements and combinations of parts as may be shown and described in connection with the apparatus herein disclosed;

In the drawings:

Fig. 1 is a vertical sectional view of an assembled transformer construction comprising one embodiment of the invention, having a secondary constructed with two turns;

Fig. 2 is a horizontal sectional view taken substantially along the line 22 of Fig. 1;

Fig. 3 is a perspective view showing the transformer housing and terminals;

Figs. 4 and 5 respectively are perspective and elevational views of the secondary of the transformer of Fig. 1;

Fig. 6 is a horizontal sectional view taken substantially along the line 6-6 of Fig. 5, and Fig. 7 a vertical sectional view substantially along the line l--'| 01' Fig. 6;

Fig. 8 is a view similar to the upper part of Fig. 1, but illustrating another embodiment of the invention wherein the secondary conductor comprises a single turn; and

Fig. 9 is a perspective view of the secondary structure of the embodiment shown in Fig. 8.

The construction as shown in Fig. 1 may comprise a container III in the form of an ordinary glazed earthenware crock adapted to be filled with a suitable transformer oil within which the transformer coil structures are submerged. The crook may rest upon a suitable supporting base ll, se-

- cured as by clamping rods I! of non-magnetic material, to a cover plate iii of insulating material, and from which the coil structures may also be suspended. A gasket It may be interposed and clamped between the upper dges of the crock I II and the cover plate It.

The coil structures may comprise a primary as at l5 formed in the example shown, oi approximately 22 turns of relatively flexible copper tubing within which a stream of cooling water is adapted to follow. The secondary structure it as shown in Fig. 1, comprises a conductor of two turns formed by making saw cuts as hereinafter described, in a copper cylinder or section of copper pipe. For purposes of cooling the secondary a piece of relatively flexible thin walled copper pipe I! is so bent as to extend along, and is brazed to the outside surfaces oi! the two secondary turns, for carrying a stream of cooling water along these turns. The term brazed" as used herein is intended to include reference to ordinary soldering.

As shown, the turns of the primary ll may be arranged close together to form a cylinder, and to prevent contact between turns, the conductor from one end to the other may be embraced in a glass fiber sleeve as at It. The primary turns may be separated from the surrounding secondary by 'a plurality oi strips of insulating material as at is, apertured at their upper and lower ends as at 20 to receive a band of glass tape or ribbon 2| which embraces longitudinally the primary coil turns and serves to hold the insulation strips in place in a manner readily apparent from Fig. 1. Additional bands or strips oi glass tape as at 22 may extend longitudinally of the primary and be tied to hold the turns together as shown.

The coil structures may be wholly or largely suspended by the electrical and cooling water connections passing out through the cover plate It. The connections for the primary may comprise hollow rods as at 23, within the lower ends of which the primar conductor tubing may be brazed as at 24. (Soldering or welding is to be considered the equivalent of "brazing" as referred to at various points herein.) Thus the stream of cooling water may be introduced through the center of one of the primary connections, thereby passing down through the cover plate and through the tubular primary winding from end to end, and thence out through the other hollow rod 23 forming the other electrical connection.

The rods 23 may be formed at their lower ends with flanges 25 adapted to hold in place porcelain bushings 28 surrounding that part of each rod which is under the cover plate. Porcelain bushings as at 21 may surround the rods 23 as they protrude above the cover plate. The upper portion oi. each rod may be threaded as at 28 to receive a clamping nut it for holding the porcelain bushings and hollow connecting rods in position in sealing relationship with respect to the cover it. Cork gaskets as at 30, II, 32 may be interpcsed at the upper and lower ends of each of the porcelain bushings for substantially sealing the connections with respect to the cover plate and bushings, against escape of oil from the transformer and also providing yielding means for preventing the clamping nuts 29, when tightened firmly in position, from cracking the porcelain bushings.

The edges at the ends of the conductor forming the secondary turns may be brazed respectively to vertically extending lugs as at 33, 84, which preferably extend up in relatively close parallel relationship and are then bent at right angles as at 35 and brazed to the lower end surfaces of copper bushings as at 38. The external surfaces of the bushings 38 may be threaded to receive clamping rings 31. The lower ends of the bushings 36 may be encircled by metal washers 38 bearing against cork washers 39, which in turn bear against the lower surface of the cover 13. The clamping rings 31 may bear against metal washers 40 which in turn bear against cork sealing washers as at 4|. The end portions of the copper cooling water tube IT for the secondary, may extend upwardly along the lugs 33 and 34 respectively and be brazed thereto as at 42. Finally, the ends of the tube l1 may be passed up through, and be brazed within the bushings 36.

The construction of the secondary will now be explained in further detail with reference more particularly to Figs. 4-7. As above stated, the secondary may be formed of a copper cylinder or section of metal pipe of copper or other metal having high electrical conductivity as well as being highly conductive of heat. In order to form such a section of pipe into two secondary turns, a saw out may be made extending first lon- :itudinally as at 45, then circumferentially as at 4 for some 320-325 about the cylinder, and thence longitudinally as at 41 to the lower edge of the cylinder, the latter longitudinal out being at an angular position spaced some 35 or 40 from the position of the initial longitudinal cut 45 at the upper part of the cylinder. While the gap which is formed at 45, 44, 41 is referred to as a saw cut, it will be understood that the metal may be cut away to form this gap other than by sawing, as for instance by a narrow grinding wheel which for the purposes hereof, is to be deemed equivalent. It will be observed that the gaps 45, 46 will serve to separate or divide the wall areas of the upper half of the cylinder to form one secondary turn, which is connected by an uncut area 48 to the lower half of the cylinder which forms the greater part of the second turn of the secondary. The second turn may be completed by brazing on an outwardly projecting rectangular piece 49, this piece in turn being brazed to a circumferentially extending piece 50. The pieces 49 and 50 thus serve to complete the second turn and bring its end around to an angular position such that the connecting lugs 33, 34 may be brought up in closely spaced parallel relationship. Such relationship is highly advantageous to prevent excessive induction between the connections at the high frequencies with which the transformer is used.

As shown, the side of the secondary at which the connecting lugs are attached, may be supported entirely by the electrical and cooling pipe terminals. It may be sometimes desirable to support the other side of the secondary as by 0. lug ll extending up through the cover I3 and held in place by a nut 42 on the upper side of the cover (Fig. 3). An oil nlling plug as at ll may be located in the cover.

'As best shown in Fig. 5 the cooling conduit I! may for example come down the lug ll and then be bent to extend along the upper turn in the manner shown, thence down along the uncut area 4| onto and around the second turn, including the piece 50 and thence back up the lug 34. The particular transformer as shown and as above described, is adapted to handle in the neighborhood of 20 kilowatts at a frequency of 400,000 cycles per second with a primary peak voltage of 7000, and a secondary peak voltage of 550. Under these conditions it has been found necessary, to avoid overheating and melting of the metal, to apply cooling means not only entirely around each turn but also to the connecting lugs and terminals. The use of flexible copper tubing bent to follow along these parts and then brazed in position thereon, has been found to be an exceptionally dependable, durable and inexpensive means for circulating the necessary cooling fluid. While some portions of the wide surfaces of each of the two secondary turns may be spaced considerably from the cooling conduit, yet adequate cooling of these portions is still accomplished provided the turns are made of copper or other material having a high heat conductivity co-eflicient. With the particular structure shown, operating at full capacity, it has been found that the maximum operating temperature in the transformer will be in the neighborhood of 100 F. with a water flow in the primary conduit of between 0.1 and 0.3 gallon per minute, and in the secondary conduit of from 1 to 2 gallons per minute.

The use of a secondary formed by cutting gaps in a metal cylinder or pipe section as above described, not only affords a simple inexpensive way of forming the secondary turns from readily available metal stock, but also the shape of these turns forming as they do, an almost complete cylindrical enclosure for the primary, makes possible an exceptionally high co-efllcient of coupling. Despite the fact that the secondary comprises but two turns, as contrasted with the primary having a much larger number of turns, the metal of the secondary turns is so spread out in cylindrical form that substantially all of the primary flux will link a secondary conductor.

It will be understood that a secondary having only a single turn or having a larger plurality of turns than two, may be made where required, by similarly forming a suitably shaped saw out or the like in a. section of pipe. For example, a secondary having three or four turns may be readily made by similar methods. Figs. 8 and 9 show a secondary having but a single turn, made of a metal cylinder or pipe section 00, formed with a gap or saw cut 6| extending longitudinally of the cylinder from end to end, and with lugs as at l2, l3 brazed along the edges of the gap. This structure may be adequately cooled as by cooling pipe 64 bent to follow along and being brazed to the single turn and the lugs in a manner similar to that above described. To prevent the metal from springing together at the saw cut, in this as well as other embodiments, one or more pieces of insulation as at may be interposed. In other respects also, the structure of Figs. 8 and 9 may be similar to that above described, like parts being referred to by the same reference numerals.

While the invention has been described in detail with respect to particular preferred examples, it will be understood by those skilled in the art after understanding th invention, that various changes and further modifications may be mad without departing from the spirit and scope of the invention, and it is intended therefore in the appended claims to cover all such changes and modifications.

What is claimed as new and desired to be secured by Letters Patent is:

1. A high frequency transformer construction comprising a cylindrical insulation crock forming a casing adapted to contain a body of oil, a cover therefor, a primary coil of numerous turns positioned on a vertical axis within such casing and substantially concentric therewith, a secondary construction comprising a cylindrical rigid self-supporting metal member surrounding the primary coil and substantially coextensive therewith, said member being formed with a narrow slot through its wall and extending along a line such as to form the wall areas into a secondary conductor of at least one turn surrounding a lurality of the primary coil turns in close inductive relation, a pair of current-carrying lug structures connected respectively to the ends of the conductor thus formed and extending upwardly in closely spaced relation and attached to the cover for suspending the secondary, and a metal cooling fluid conduit soldered around the outside surface of said secondary, with its ends communicating with exterior cooling fluid connections by way of cavities formed through said lug structures.

2. In a high frequency transformer, a secondary construction comprising a vertically disposed cylindrical metal member, a narrow slot being formed through the walls of such member along a line extending first longitudinally, starting from the edge at one end of the member, then extending generally circumferentially for somewhat less than 360 about the member, and then further longitudinally to the edge at the other end of the member, to thereby separate the wall areas of the member into a secondary conductor of nearly two turns, an additional conductive portion fixed to one end of such conductor and extending generally circumferentially in spaced relation to said wall areas for a distance sumcient to substantially complete the two turns, and a pair of rigid current-carrying members forming terminal connections for the secondary extending vertically in closely spaced relation respectively from the ends of the two turns thus formed.

3. A high frequency transformer construction comprising a non-magnetic casing adapted to be filled with oil, a rimary coil of numerous turns positioned on a vertical axis within such casing, a secondary construction comprising a vertically disposed cylindrical section of sheet-like metal surrounding said primary in closely spaced relation, said section having a narrow gap extending longitudinally from top to bottom along one side thereof, thereby forming thereof a one-tum secondary conductor linked by the greater part of the flux of all the turns of the primary coil, a pair of conductive bars respectively fixed along the edges of said gap and extending up vertically in :closely spaced relation to form terminals and supporting means for the secondary, and a metal cooling fluid conduit soldered around the outside surface of said secondary, with its ends communicating with exterior cooling fluid connections by way of cavities fonned through said supporting terminals.

4. A high frequency transformer construction comprising an oil-filled non-magnetic casing including a cover, primary and secondary constructions suspended from the cover, in position for one to surround the other in closely spaced relation, and hollow terminal bushing assemblies for the primary and the secondary, extending through the cover in clamping and sealing relation thereto, the primary and secondary conductors being formed with cooling fluid cavities extending therealong and communicating at their ends respectively with said hollow bushings to provide cooling fluid connections substantially coaxial with the electrical terminals.

5. In a high frequency transformer, a secondary construction comprising a cylindrical metal member, a narrow slot being formed through the walls of such member along a line extending first longitudinally starting from the edge at one end of the member, then extending generally circumferentially for somewhat less than 360 about the member, and then further longitudinally to the edge at the other end of the memher, to thereby separate the wall areas of the member into a secondary conductor of nearly two turns, an additional conductive portion fixed on. on end of such conductor and extending generally circumferentially in spaced relation to said wall areas for a distance sufficient to substantially complete the two turns, a pair of terminal connections for the secondary secured respectively to the ends of the two turns thus formed. and a metal cooling fluid conduit xtending from one of said terminal connections, thenc along said turns and into the other terminal connection, in close heat conductive relationship with said turns, said conduit passing from one of said turns onto the other in the space provided between said additional conductive portion and said wall areas.

WALLACE C. RUDD. 

